When the surface of a workpiece is subjected to the conventional deposition treatment such as arc discharge or sputtering, the workpiece temperature rises because high-energy particles such as metal ions or gas ions collide with the workpiece. Therefore, the deposition treatment needs to be performed while cooling the workpiece.
However, the workpieces are usually placed on a rotating table and revolved around a vertical axis while performing the deposition treatment. This means that the workpieces do not remain stationary on the same places. Therefore, even when a cooling unit for cooling a chamber is disposed inside the chamber, the cooling unit cannot be brought into contact with the revolving workpieces and a constant distance cannot be maintained between the cooling unit and workpieces. The resultant problem is that the workpieces cannot be stably cooled.
Accordingly, a deposition device has been suggested in which a cooling unit is placed on a rotating table inside a vacuum chamber and workpieces are cooled while rotating the cooling unit together with the workpieces, as described in Patent Literature 1. In this deposition device, the cylindrical cooling unit is installed vertically and fixed in the center of the upper surface of the rotating table. A plurality of workpieces is arranged side by side on the circumferential side of the upper surface of the rotating table. Therefore, when the rotating table is rotated, the cooling unit is rotated in the center of the upper surface of the rotating table. At the same time, the plurality of workpieces is revolved around the cooling unit.
The cooling unit is connected to refrigerant piping attached to the chamber wall, and a refrigerant, such as water, circulates through the refrigerant piping between the cooling unit and the chamber. As a result, the cooling unit is cooled. The outer circumferential surface of the cylindrical cooling unit functions as a cooling surface that faces the workpieces at all times, absorbs the radiant heat from the workpieces, and cools the workplaces. Even when the workpieces rotate together with the rotating table, they face the cooling unit at all times. Therefore, although the workpieces and cooling unit are set apart, the radiant heat from the workpieces to the cooling unit can be continuously transferred thereto.
The refrigerant piping and cooling unit are connected through a rotary joint. As a result, the refrigerant, such as cooling water, is continuously supplied through the rotary joint to the cooling unit rotating together with the rotating table, and the refrigerant can be discharged from the cooling unit. The rotary joint is configured such that a fluid is circulated between two physical bodies rotating relative to each other.
The deposition device has a configuration in which the refrigerant is supplied to and discharged from the cooling unit, which rotates together with the rotating table, through the rotary joint. Since the rotary joint in which the refrigerant circulates is thus used inside the vacuum chamber, there is a high risk of the refrigerant leaking from the rotary joint. Further, the device structure should be made more complex by including a differential evacuation mechanism in order to increase the sealing ability of the rotary joint.
While the rotating table is rotated, the cooling unit rotates on the center of the upper surface of the rotating table. At the same time, a plurality of workpieces revolves around the periphery of the cooling unit synchronously with the rotation of the cooling unit. Therefore, the relative positional relationship between the cooling unit and the workpieces arranged on the periphery of the cooling unit does not change. Thus, certain portions of the cooling surface on the outer circumference of the cooling unit are maintained in a state of facing the workpieces, whereas other portions are maintained in a state of not facing the workpieces. Therefore, the cooling surface facing the workpieces is exposed at all times to the radiant heat from the workpieces and cannot be maintained in a low-temperature state. Meanwhile, the cooling surface that does not face the workpieces is in the low-temperature state at all times. Such a state of the cooling surfaces does not conform to the purpose of the cooling unit which is to ensure that the cooling surface with the lowest temperature faces and cools the workpieces. As a consequence, the cooking efficiency of the cooling unit is degraded. In other words, with the above-described structure, the cooling unit and the workpieces rotate together. Therefore, the portions of the cooling surface that face the workpieces receive the radiant heat from the workpieces at all times and are at a temperature higher than that of the cooling surface that does not face the workpieces. Meanwhile, the surface that does not face the workpieces, does not receive the radiant heat and maintains a low-temperature state. As a result, the cooling efficiency of the entire cooling unit is degraded. The resultant problem is that the cooling surface of the cooling unit is not used effectively and that the efficiency of cooling the workpieces with the cooling unit is difficult to increase.